Notes on Myriapoda, Crustaceans, and Chelicerata

Subphylum Myriapoda

  • Includes arthropods with legs ranging from 10 to 750.
  • Comprises approximately 13,000 species.
    • Common examples: millipedes and centipedes.
  • Habitats: All myriapods are terrestrial and prefer humid environments.

Key Characteristics of Myriapods

  • Example Species:
    • Centipede (Scutigera coleoptrata):
    • Has up to 15 pairs of legs.
    • North American millipede (Narceus americanus):
    • Known for having many legs (not a thousand despite its name).

Crustaceans

  • Dominant aquatic arthropods, including:
    • Shrimp
    • Lobsters
    • Crabs
    • Crayfish
  • Approximately 47,000 described crustacean species.
    • Some terrestrial species: pill bugs and sow bugs.

Body Plan of Crustaceans

  • Basic body layout is similar to that of Hexapoda with three main regions: head, thorax, and abdomen.
  • In some species, the head and thorax fuse to form a cephalothorax.
    • This region is covered by a plate known as the carapace.
  • Exoskeleton Composition: Many crustaceans have an exoskeleton infused with calcium carbonate for added strength.

Circulatory System

  • Crustaceans possess an open circulatory system in which blood is pumped into a hemocoel by the:
    • Dorsal heart.

Reproductive Characteristics

  • Typically exhibit separate sexes.
  • Some species, like barnacles, may be hermaphroditic.
  • Serial hermaphroditism can occur, allowing the gonad to switch from producing sperm to ova.
  • Larval stages are part of the developmental process for many crustaceans.

Feeding Habits

  • Most crustaceans are carnivorous.
  • Also common are detritivores and filter feeders.

Subphylum Chelicerata

  • Includes animals such as:
    • Spiders
    • Scorpions
    • Horseshoe crabs
    • Sea spiders
  • About 103,000 described species within Chelicerata.
  • Primarily terrestrial, but includes some marine species.

Body Structure of Chelicerates

  • Body is often divided into two parts; a distinct head may not always be apparent.
  • The name Chelicerata derives from their chelicerae:
    • Specialized mouthparts used mainly for feeding.
    • In spiders, chelicerae are modified to inject venom into prey.

Circulatory System

  • Like other arthropods, chelicerates have an open circulatory system.
    • They possess a tube-like heart that pumps blood into the large hemocoel surrounding internal organs.

Respiration

  • Aquatic chelicerates utilize gill respiration.
  • Terrestrial species respire using:
    • Tracheae
    • Book lungs for gas exchange.